The “Z” Sound
This is a “Skinny Air” sound.
The back teeth should be nearly closed. Spread the lips in a smile position ( your lips should be stretched and skinny ). Raise the tongue-tip behind the teeth near the gum ridge. The breath stream travels over the grooved tongue. The air space is skinny.
This is a “Noisy brother” the vocal cords should vibrate, be sure to listen for the “buzz” when you say this sound.